1. Field of the Invention
The present invention relates to the structure and manufacture of laminated parts used in electric motors or generators. More particularly, the field of the invention is that of laminas adapted to be stacked and used in the manufacture of rotors and stators.
2. Description of the Related Art
Rotor and stator manufacture employing stacked laminas is well known in the art. Typically, the laminas are blanked from continuous strip stock and then stacked and bound together to form the rotor or stator. Progressive die assemblies for producing stator or rotor laminations are well known, wherein a strip of lamination material is fed through a sequence of punching steps to progressively form the laminas to the desired end configuration. It is also well known to form arcuate interlock tabs in the laminas which extend below the lamina tower surface and engage a slot formed in the next lower lamina. In this manner, a plurality of laminas may be formed from a single strip stock and interconnected by means of the interlock tabs.
Stator stacks include openings around the inner periphery of the stack which are shaped to receive the stator windings, with the openings extending longitudinally straight down the bound stator stack. The laminas of the rotor, however, include a plurality of skewed conductor slots which are formed around the periphery of the rotor stack in arcuately spaced relation to one another, by rotationally indexing the laminas with respect to the rotor stack. Indexing involves rotating the rotor stack with respect to the last produced lamina by a predetermined rotational increment so that, when the laminas are combined in a stack, the space defined by adjacent conductor slots are skewed or slanted relative to the stack axis. Skew inaccuracies and/or excessive adjustment time results from many prior art systems. Also, variations in the thickness of the lamina may cause unbalanced stacks to be formed. In order to compensate for these problems, a system for compensating for the nonuniform thickness was developed which rotates the stacked laminas to compensate for variations in thickness while still properly skewing the conductor slots, as described in U.S. Pat. Nos. 4,738,020; 4,619,028; 5,087,849 and copending U.S. patent application Ser. No. 07/724,866, filed Jul. 21, 1991, entitled "APPARATUS AND METHOD FOR MANUFACTURING LAMINATED PARTS" now U.S. Pat. No. 5,123,155, all assigned to the assignee of the present invention and which disclosures are incorporated herein by reference.
However, the laminas must be electrically insulated from each other in order to function properly in electric motors or generators. One known method involves the use of an annealing oven to treat the individual laminas so that a thin non-conductive or insulative layer forms on the generally planar surfaces of the laminas, e.g., an oxidation layer formed by bluing or annealing. Another beneficial effect of the annealing oven is that many of the internal stresses are removed from the laminas, and the grain of the metallic material of the laminas is reoriented.
In order to form the insulative or non-conductive layer, each individual lamina must be sufficiently spaced apart between the planar surfaces of the laminas. Although the strip stock may be annealed prior to punching, any subsequent cutting or bending in the manufacture of the laminas may create gaps in the non-conductive layer and/or further stress the material. Therefore, the laminas are conventionally subject to annealing after they are manufactured and stacked. One known method involves the use of spacers which are positioned between the laminas, or coating on the laminas, which burn off in the annealing oven. Another known method involves only loosely stacking the laminas so that the planar surfaces are not held together and thus do not block fluids or the oven atmosphere from contacting the planar surfaces.
However, these known methods contain inherent deficiencies. Spacers positioned between laminates tend to burn off in the annealing oven and produce fumes which may interfere or contaminate the oxidation or other process which forms a non-conductive layer on each planar surface. Subjecting loose stacks to annealing causes thermal expansion which often misaligns the stacks and introduces errors in subsequent manufacturing.
What is needed in the art is a lamina stack structure which may be successfully annealed.
An additional need exists for such a lamina stack which may be successfully treated in an annealing oven without creation of products of combustion.
Also needed is a lamina stack structure which may withstand the temperatures of the annealing oven with structural integrity.
Further needed is a method of manufacturing such a lamina stack structure.
Another need is for an apparatus for manufacturing such a lamina stack structure.